The present invention relates to the general field of soundproofing panels of the so-called “passive” type operating on the basis of Helmholtz resonators.
It finds an advantageous application in the aviation sector, in particular for the ducts of a turbomachine that are subjected to high temperatures.
In the field of aviation, soundproofing panels are used to reduce the level of sound emitted by the turbomachines of an airplane. These panels are generally disposed directly as flow walls in order to attenuate the sound energy generated by the various components of the turbomachine.
The present invention seeks more particularly to apply such soundproofing panels to the hot ducts of a turbomachine, for example at turbine outlets or at the exhaust nozzle.
In this context, it is therefore necessary to make soundproofing panels that withstand the high temperatures of the ducts and that enable sound levels to be reduced without thereby penalizing the strength, the weight, or the size of the turbomachine.
A known method of making soundproofing panels is described in patent FR 2 775 216. That document purposes making soundproofing panels by means of a structure sandwiched between two skins and having cells that are arranged as Helmholtz resonators. The Helmholtz resonators are implemented in the form of layers of hollow beads that are stuck to one another and to the walls of the structure by a resin type binder.
Apart from the difficulty in making it, the soundproofing panel described in that patent presents certain other drawbacks for applications at high temperature.
That soundproofing panel presents poor thermal behavior when it is subjected to high temperatures, and the use of a binder between the beads leads to problems of galvanic coupling, leading in turn to problems with points of corrosion.
In addition, when processing using cavities of large dimensions, the method disclosed is difficult to adapt to implementing soundproofing panels with acoustic characteristics that vary. For example, it is difficult to vary the thicknesses of the layers of beads within a given cell so that the acoustic characteristics of the cell remain substantially constant.